A source told IBTimes UK that when the SNB said it would no longer cap the Swiss franc's value against the euro, sending the currency soaring as much as 30% in a chaotic day of trading, Barclays was unable to fulfil client orders in time.

Barclays declined to comment.

The FX market is one of the largest and most liquid markets in the world, with a daily average turnover of $5.3tn, 40% of which takes place in London.